Polymeric flocculants are commonly used for the separation of fine particulate matter from a liquid in which it is suspended. This separation occurs by the coalescence of fine particles to form larger aggregates that, by virtue of increased size, will settle at a reasonable rate. Thus, the purification of a liquid in this manner is accomplished by the process of sedimentation, which is conducted in large vessels (settlers or clarifiers) specifically designed for this purpose. It is essential that the flocculant that is added to the liquid being purified does not cause any deleterious effects, in particular, foaming of the liquid.
Foaming can result in a number of unwanted effects, for example gross interference with the sedimentation process due to the flotation (rather than sedimentation) of the solid particles, resulting in reduced efficiency and other negative "downstream" effects. Other deleterious effects of foaming include loss of solids due to solids-laden foam overflowing the vessel, resulting in lost production and creation of a safety hazard, and severe interference with instruments designed to control the sedimentation process including instruments for bed level detection, overflow clarity measurement, and the like.
Latex polymer flocculants are typically prepared using a water-in-oil emulsion polymerization technique whereby aqueous solutions of water-soluble vinyl addition polymers can be rapidly produced. This procedure is well known, and can be exemplified by U.S. Pat. Nos. 3,284,393; Re 28,576; 3,624,019; 3,767,629; 3,826,771; 3,915,920; 3,996,180; 3,979,348; 4,024,097; 3,997,492; Re 28,474 and 3,734,873 among others. A typical water-in-oil emulsion polymer contains a finely divided water soluble polymer dispersed in an oil.
To stabilize such polymers in oil, it is necessary to add one or more emulsifiers to the latex. Traditionally, these emulsifiers have been fatty acids or fatty acid esters. However, the use of a latex polymer that contains such emulsifiers can often introduce new problems such as foaming into an aqueous system to which the latex polymer is added as a treatment. Losses due to foaming have heretofore been accepted as an unavoidable side effect of using latex polymer flocculants, except in cases of severe foaming in which additional anti-foam agents are added to the system.
Flocculation and sedimentation techniques employing latex polymer flocculants are widely used in the mineral processing industries, water and waste treatment and in the production of pulp and paper. Therefore, there is an ongoing need for the development of new non-foaming flocculants for use in these applications.